1. Field of the Invention
The present invention relates generally to optical devices such as lasers, and fiber optic data transmission systems employing the same, and particularly to a novel variable optical signal attenuator device for use in such systems that implements a wavelength-locked loop servo-control circuit.
2. Description of the Prior Art
Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) are light-wave application technologies that enable multiple wavelengths (colors of light) to be paralleled into the same optical fiber with each wavelength potentially assigned its own data diagnostics. Currently, WDM and DWDM products combine many different data links over a single pair of optical fibers by re-modulating the data onto a set of lasers, which are tuned to a very specific wavelength (within 0.8 nm tolerance, following industry standards). On current products, up to 32 wavelengths of light can be combined over a single fiber link with more wavelengths contemplated for future applications. The wavelengths are combined by passing light through a series of thin film interference filters, which consist of multi-layer coatings on a glass substrate, pigtailed with optical fibers. The filters combine multiple wavelengths into a single fiber path, and also separate them again at the far end of the multiplexed link. Filters may also be used at intermediate points to add or drop wavelength channels from the optical network.
Optical communication links in systems employing WDM or, optical networks in general, require amplification to extend their distances. However, for some optical network applications it is advantageous to be able to provide for the attenuation of optical signals. For example, optical attenuator devices are often implemented to control light levels in fiber optic networks in order to prevent saturation and other effects.
It would thus be highly desirable to provide an optical attenuator device in an optical system that does not comprise a separate optical component in the network.
It would be further highly desirable to provide a variable optical attenuator device in an optical system that may be easily integrated in a simple feedback circuit without requiring a separate optical component in the network.
It would be highly desirable to provide a servo-control feedback loop for dynamically tracking the center wavelength of an optical signal to the peak of an optical filter passband with high accuracy to enable precise optical attenuation of optical signals.
It is therefore an object of the present invention to provide an optical attenuator device in an optical system that does not comprise a separate optical component in the network.
It is another object of the present invention to provide variable optical attenuator device in an optical system that may be easily integrated in a simple feedback circuit without requiring a separate optical component in the network.
It is a further object of the present invention to provide a servo-control feedback loop for dynamically tracking the center wavelength of an optical signal to the peak of an optical filter passband with high accuracy to enable precise optical attenuation of optical signals.
It is still another object of the present invention to provide a servo/feedback loop, referred to as a xe2x80x9cwavelength-locked loop,xe2x80x9d that provides tracking of the center wavelength of the optical signal to the peak of an optical filter passband to achieve a desired attenuation of the optical signal for fiber optic data communication systems.
According to a preferred embodiment of the invention, there is provided a system and method for attenuating optical signals communicated in an optical network comprising: an optical signal generator for generating optical signals, each optical signal having a peaked spectrum function including a center wavelength; an optical filter element for receiving and filtering an optical signal, the optical filter element exhibiting a peaked passband function including a center wavelength; and, a wavelength-locked loop servo-control circuit for enabling real time alignment of the optical signal center wavelength with the peaked passband function of the optical filter, the optical signal center wavelength capable of being aligned at a wavelength corresponding to maximum overlap with the center wavelength of the peaked passband function of the optical filter for maximum transfer of the output optical signal by the filter element and minimum overlap with the peaked passband function of the optical filter so that the output optical signal may be attenuated in the optical system.
Advantageously, the wavelength-locked loop for providing attenuating optical signals according to the invention, is advantageous for application areas such as radar and sonar signal processing, image sampling and transmission, holographic storage, and other areas while preserving life of the optical signal generator devices. Furthermore, the VOA system of the invention may be employed to provide gain equalization in a laser array or bank of lasers and, additionally, may be applicable to single comb filters which are comprised of periodic or a periodic spectral passbands allowing channels to be xe2x80x98provisionedxe2x80x99 and attenuated in a controlled pattern, e.g., in a xe2x80x98tilted spectralxe2x80x99 function or uniformly to equalize the optical power across all wavelengths in the WDM system, particularly to compensate for optical amplifier effects.